1. Field of the Invention
This invention relates to a process for controlling the etching of a silicon substrate by atomic hydrogen and the production of a modified silicon device. More specifically, this process involves implanting a boron dopant into the surface of the silicon substrate and subsequently etching the undoped portions of the substrate with atomic hydrogen.
2. Brief Description of the Prior Art
The incorporation of boron into silicon is well known. Boron is used commonly as a bulk dopant of silicon. Modification of the surface atomic and electronic structure of silicon by foreign atoms such as for example boron, phosphorus or arsenic, is generally known to influence silicon etching mechanisms involving etching reagents other than atomic hydrogen. Etching of the silicon surface by atomic hydrogen involves the removal of surface silicon atoms. The breaking of adatom silicon-silicon backbonds forms silicon dihydride and silicon trihydride species on the silicon surface. These adatom hydrides are believed to be the precursor species for the gas phase etching product, silane (SiH.sub.4).
U.S. Pat. No. 3,721,593 discloses a process for stopping the etching action of the etching agent, potassium hydroxide, in liquid phase. The process involves a silicon layer doped with boron.
U.S. Pat. No. 4,601,779 discloses a process that includes forming an etch-stop layer in silicon by implanting boron ions into the silicon. The etchant is a solution of hydrofluoric, nitric and acetic acid.
U.S. Pat. No. 4,131,985 discloses a method of making a semiconductor structure through formation of a semiconductor device on a surface of a polished silicon slice. This patent states that the device may be framed with a diffusion pattern of boron prior to effecting etching using a conventional isotropic etch.
U.S. Pat. No. 4,584,055 discloses a method of manufacturing a semiconductor device which includes doping an impurity ion, such as boron, into a semiconductor layer and subsequently etching the semiconductor layer using potassium hydroxide or amine, pyrocatechol and water as an etchant. This patent states that the etching rate is extremely low in portions where the boron ion is highly doped.
U.S. Pat. No. 4,313,773 discloses a method of boron doping a silicon body wherein the silicon body is exposed to a gas mixture containing BBr.sub.3 and oxygen prior to etching. This method uses hydrofluoric acid diluted with water and then aqueous sulfuric acid/potassium permanganate solution as an etchant.
U.S. Pat. No. 4,092,209 discloses a method for rendering a surface of a body of silicon unetchable that includes bombarding the silicon surface with phosphorus or boron. This patent states that it is known that the etch rate is substantially reduced when boron is placed in the silicon semiconductor by solid-to-solid diffusion, gaseous diffusion or ion implantation. The etching reagent is potassium hydroxide solution.
U.S. Pat. No. 4,718,973 discloses a method for implanting a dopant such as phosphorus or arsenic within a polysilicon layer such that the dopant is heavily concentrated at the polysilicon surface. This patent states that plasma etching is subsequently performed by using a mixture of a fluorine and chlorine etchant gas, and that the implanted regions are protected from etching.
In spite of these prior art disclosures, there remains a very real and substantial need for a process for the spatially selective gas phase dry etching of silicon with atomic hydrogen. None of the prior processes involves the use of atomic hydrogen as the etching reagent.